1. Field of the Invention
The present invention relates to a hydrogen chloride supply system, an air pollution control system, and a hydrogen chloride supply control system.
2. Description of the Related Art
Conventionally, various systems for removing mercury in flue gas have been considered because, boilers serving as combustion apparatuses in power stations and other facilities discharge flue gas containing highly toxic mercury.
A boiler generally includes a wet desulfurization apparatus for removing sulfur content in flue gas. In flue gas treatment facilities including such a boiler provided with a desulfurization apparatus that serves an exhaust gas treatment apparatus, as chlorine (Cl) content increases in flue gas, the ratio of water-soluble divalent metallic mercury increases. This facilitates collection of the mercury with the desulfurization apparatus, as is well known.
In recent years, various proposals have been made on denitration apparatuses that reduce NOx, and on methods and apparatuses for treating the metallic mercury in combination with a wet desulfurization apparatus that uses an alkali absorbing solution as SOx absorbent.
As treatment of metallic mercury in flue gas, removal methods using an absorbent such as activated carbon or a selenium filter have been known. These methods, however, require special means for absorption removal, and are not suitable for treatment of a large volume of flue gas, such as flue gas in power stations.
As a method for treating metallic mercury in a large volume of flue gas, methods have been proposed that include: gas-atomizing a chlorinating agent in a flue at an upstream process in a high-temperature denitration apparatus, oxidizing (chlorinating) the mercury on a denitration catalyst to be aqueous hydrogen chloride, and then absorbing it in a downstream wet desulfurization apparatus (for example, see Japanese Patent Application Laid-open No. 10-230137). Apparatuses and techniques for spraying gas in a flue have been commercialized as NH3 spray devices of denitration apparatuses, and the same means can be used for gas atomization of a chlorinating agent.
When employing the mercury removal system that sprays hydrogen chloride or the like as proposed above, 35% hydrochloric acid is evaporated in a vaporizer. Accordingly, the resulting by-product, i.e., dilute hydrochloric acid, is discharged by an amount equivalent to about 80% of the feedstock (35% hydrochloric acid). This poses a problem that the dilute hydrochloric acid results in a waste product for the power station.
The chlorine concentration varies depending on the type of coal used in the power station (i.e., coal type). Even when a coal type with high chloride concentration is used, 29 tons of 35% concentrated hydrochloric acid is necessary per day, and dilute hydrochloric acid is discharged by an amount equivalent to that of the 35% concentrated hydrochloric acid. Thus, to establish recycling plants as ancillary facilities to treat the dilute hydrochloric acid as a waste product, a set of plants needs to be established. This increases costs for establishing and maintaining the plants.
It is also considered to establish recycling plants within power generating facilities. This requires, however, substantial addition in treatment processes because non volatile materials are circulated and concentrated in the treatment of the dilute hydrochloric acid.
Thus, there is a demand to make dilute hydrochloric acid, discharged as a by-product, available for reutilization and recycle it, without disposing it.
The present invention is made in view of the above problems, and has an object to provide a hydrogen chloride supply system, an air pollution control system, and a hydrogen chloride supply control system that require low operating costs.